You might look at the conclusion of a research study in the title here as just too obvious, but it's not as simple as cuddling up because it's cold. We know that birth rates peak in September, but is that because it's cold in the winter, or because people get frisky during the Christmas holidays? It turns out that when you study the phenomenon globally, the holiday has more to do with it than the climate. Birth rates peak in September in the Southern Hemisphere, too, but only in countries in which the majority of people observe Christmas.
The analysis revealed that interest in sex peaks significantly during major cultural or religious celebrations—based upon a greater use of the word "sex" or other sexual terms in web searches. These peaks broadly corresponded to an increase in births nine months later in countries with available birth-rate data.
Moreover, the effect was observed in two different cultures, with the greatest spike occurring during major holiday celebrations: Christmas in Christian-majority countries and Eid-al-Fitr, the celebration that marks the end of Ramadan, in Muslim-majority countries.
The use of data from the Northern and Southern hemispheres is notable since past analyses tended to focus on smaller geographic areas in the Western and Northern hemispheres. The case of Eid-al-Fitr is significant because the holiday does not occur on the same day each year, but the measured effect still shifts accordingly, following a clear cultural pattern.
In fact, you can detect the dominant religion of a country by looking at the peak birth month, as in the above map. Thanksgiving and Easter did not significantly affect the birth rate. Read more about the study at PhysOrg. -via Digg
(Image credit: Ian Wood, Indiana University)